1. Field of the Invention
The present invention relates to a drive transmission device including a gear train which transmits rotational drive from a drive source to a drive target, and to a sheet feeder and an image forming apparatus each including the drive transmission device.
2. Description of the Related Art
There is a known sheet feeder which reverses the direction of feeding force applied to a sheet fed to a predetermined feed path in an image forming device to thereby change the direction of the sheet and switch back the sheet.
This type of sheet feeder includes a roller member capable of being driven to rotate in both the forward and reverse directions. When driven to rotate in a first rotation direction, the roller member applies to the sheet a feeding force the same in direction as the feeding force applied to feed the sheet to the predetermined feed path. When driven to rotate in a second rotation direction opposite to the first rotation direction with predetermined timing, the roller member switches back the sheet.
Further, there is a known drive transmission device (hereinafter referred to as the first known drive transmission device) capable of transmitting both rotational drive in the forward direction and rotational drive in the reverse direction to a roller member as the drive target by changing the rotation direction of a drive motor serving as the drive source.
Another known drive transmission device (hereinafter referred to as the second known drive transmission device) includes, as the gear train for transmitting the rotational drive from the drive motor to the roller member, two gear trains which transmit rotational drives in opposite directions, and each of which is provided with a clutch mechanism for switching between connection and disconnection of the drive transmission.
Still another known drive transmission device (hereinafter referred to as the third background drive transmission device) includes a gear train which transmits the rotational drive from the drive source to the roller member, and in which the extreme upstream gear in the drive transmission direction serves as a drive input gear. The third known drive transmission device further includes a first drive transmission gear train and a second drive transmission gear train. The first drive transmission gear train includes an odd number of gears, and forms a first path for transmitting the rotational drive of the drive input gear. The second drive transmission gear train includes an even number of gears, and forms, separately from the first path of the first drive transmission gear train, a second path for transmitting the rotational drive of the drive input gear. The third known drive transmission device further includes a movable gear (also referred to as a swing gear) movable between a first drive transmission position and a second drive transmission position. At the first drive transmission position, the movable gear meshes with the extreme downstream gear of the first drive transmission gear train in the drive transmission direction. At the second drive transmission position, the movable gear meshes with the extreme downstream gear of the second drive transmission gear train in the drive transmission direction. Located at the first drive transmission position or the second drive transmission position, the movable gear transmits the drive to a gear which inputs the drive to the roller member.
According to the first known drive transmission device, if the drive motor also functions as the drive source of another rotary member as well as the drive source of the roller member, the roller member is not allowed to receive the input of the rotational drive in the reverse direction or stop rotating, when the another rotary member needs to receive the input of the rotational drive in the forward direction. Consequently, the degree of freedom in controlling the rotational drive of the roller member is reduced.
The second known drive transmission device allows the rotational drive in a fixed direction input from the drive motor to be transmitted to the roller member either as the rotational drive in the forward direction or the rotational drive in the reverse direction in accordance with switching between the clutch mechanisms for connecting the drive transmission. If the drive motor also functions as the drive source of another rotary member, and if the another rotary member needs to receive the input of the rotational drive in the forward direction, therefore, the roller member is allowed to receive the input of the rotational drive in the reverse direction in accordance with switching between the clutch mechanisms for connecting the drive transmission. Further, if the two clutch mechanisms are disengaged, the rotational drive of the roller member is allowed to be stopped, even when the rotary member needs to receive the input of the rotational drive in the forward direction. According to the second known drive transmission device, therefore, the degree of freedom in controlling the rotational drive of the roller member is increased, when the drive motor also functions as the drive source of another rotary member.
A clutch mechanism, however, engages and disengages, with at least one gear moving between a position for connecting the drive and a position for disconnecting the drive. The second known drive transmission device includes two clutch mechanisms. This configuration increases the device size and complicates the device structure.
The third known drive transmission device switches the position of the movable gear between the first drive transmission position and the second drive transmission position, to thereby change the gear train which transmits the rotational drive to the movable gear. Further, the first drive transmission gear train includes an odd number of gears, and the second drive transmission gear train includes an even number of gears. Therefore, the rotation direction of the rotational drive transmitted to the movable gear is different between the first drive transmission gear train and the second drive transmission gear train. With this change of the gear train which transmits the rotational drive to the movable gear, therefore, the rotational drive in the fixed direction input from the drive motor is allowed to be transmitted to the roller member either as the rotational drive in the forward direction or the rotational drive in the reverse direction. If the drive motor also functions as the drive source of another rotary member, and if the another rotary member needs to receive the input of the rotational drive in the forward direction, therefore, the roller member is allowed to receive the input of the rotational drive in the reverse direction in accordance with switching of the position of the movable gear between the first drive transmission position and the second drive transmission position.
Further, in the third known drive transmission device, the movable gear is the only gear to be moved to change the rotation direction of the roller member. Therefore, the increase in device size and the complication of the device structure are minimized, as compared with the second known drive transmission device, which moves two gears.
In the third known drive transmission device, however, the position of the movable gear is either one of the first drive transmission position and the second drive transmission position. When the drive motor is driven, therefore, either one of the rotational drive in the forward direction and the rotational drive in the reverse direction is input to the roller member. Accordingly, when the rotational drive in the forward direction needs to be input to another rotary member, which shares the drive source with the roller member, the rotational drive of the roller member is not allowed to be stopped. As a result, the degree of freedom in controlling the rotational drive of the roller member is reduced.
The above-described issues are not limited to the drive transmission device which transmits the drive to the roller member as the drive target, and may arise in any device which transmits the rotational drive input from the drive source to the drive target via a gear train.